Learn about stormwater and how to reduce pollution

How does stormwater impact us?

1/3 of the pollution in Washington State's water is from stormwater runoff.

Using Weed and Feed?

23 pesticides can be found in our streams during any given rainstorm.

5 of those exceed the level that is considered safe for aquatic life.

After 1 inch of rain...

748 gallons of stormwater runs off a 1,200 square foot roof

27,000 gallons of stormwater runs off a 1-acre parking lot

Other stormwater impacts

50% of all salmon and steelhead runs in Puget Sound are considered unhealthy.

Washington State is the number 1 producer of oysters, clams and mussels in the U.S.

32% of the certified commercial shellfish growing areas in Puget Sound, or 140,000 total acres, have been partially or completely closed due to water pollution since 1980.

Reduce stormwater and its pollution at home

Introduction to stormwater in King County
Learn about the science of stormwater, common problems related to stormwater including causes and solutions, homeowner tips, regulations, and how to get help from King County.

KCRTS hydrologic and KCBW hydraulic modeling software

The King County Runoff Time Series (KCRTS) hydrologic model is a required methodology under the 1998 King County Surface Water Design Manual for sizing detention and infiltration flow control facilities.

The King County Backwater (KCBW) Program is a standard step backwater analysis program for pipe networks, culverts, and simple open channels.

Stormwater infrastructure

Wastewater system

Combined sewer overflow status map
Some old segments of our regional sewers were designed to drain stormwater too, but these combined systems occasionally flood in big downpours. Combined sewers were designed to let diluted wastewater overflow untreated into rivers, lakes or Puget Sound to avoid sewage backups in homes and businesses.

Stormwater projects and plans

King County Stormwater Management Program (SWMP)
Describes King County's action plan to comply with the National Pollutant Discharge Elimination System (NPDES) phase I municipal stormwater permit issued by the Washington State Department of Ecology.

King County climate change plan
How King County seeks to reduce greenhouse gas emissions, adapt to projected climate change impacts, and embed mitigation and adaptation into county policy decisions. The plan incorporates issues, goals and actions related to stormwater.

Stormwater resources and references
Links to regulatory agencies, environmental organizations, King County stormwater staff directory, and other resources for information on stormwater and related water resource topics.

Interactive map - stormwater complaints, facilities, projects and studies
Note: this link will open a new browser window
View map layers related to stormwater by clicking the layers icon , expand the "Stormwater Services" group of layers and check those layers you want to view and query including drainage complaints, stormwater facilities, neighborhood drainage projects, and stormwater studies among other things. Click a symbol or area to display the data about it.

Stormwater treatment and flow controls map - Post 1990 (17.5 Mb)
This map shows parcels in King County that were developed after 1990, when stormwater treatment controls and substantially more effective stormwater flow controls started to be required for new development. Thus the map presents a general graphic illustration of where modern stormwater controls are presumed to have been implemented and where development has occurred with no treatment control and little or no flow control. Note, the map is based on the year of latest development and does not represent actual stormwater control. In addition, the area presumed to have modern stormwater controls is likely smaller than what is shown because not all incorporated areas began requiring such controls when unincorporated King County did in 1990.